1. Field of the Invention
The present invention relates to a system for measuring in real time amounts of dry soot (e.g., carbon particulates) and a soluble organic fraction (referred hereinafter to as an SOF) which are contained in an exhaust gas from a diesel engine.
2. Description of the Prior Art
There is a tendency for vehicles equipped with diesel engines to increase in number because of the better fuel consumption rate of this type of engine compared with a gasoline engine. However, diesel engines exhaust larger amounts of particulates than those discharged by gasoline engines. The exhausted particulates are a serious problem from the viewpoint of environmental pollution. For this reason, the governments of some countries, such as the United States of America, are inclined to provide severe regulations concerning the quantities of particulates exhausted from diesel engines. Under these circumstances, it is particularly important to determine the particulate exhaust characteristics of vehicles and, more particularly, the particulate exhaust of each vehicle, which varies from moment to moment.
The particulates exhausted from the diesel engine are classified as dry soot and SOF. It is considered that the SOF is more harmful than the dry soot for human health, because the former may include a carcinogenic substance. Therefore, there is a strong demand that the amount of SOF in the exhausted gas be estimated separately from the amount of dry soot therein.
A conventional measurement to determine the amount of dry soot and SOF in the exhausted gas is performed in the following manner: Particulates in an exhaust gas are collected by a filter. The temperature and humidity of the collected particulates are controlled and the particulates are weighed by a chemical balance, thereby determining the concentration of the total particulates. Then, the SOF is extracted by the Soxhlet extraction method from the particulates deposited on the filter and the residue is weighed to determine the concentrations of dry soot and SOF. However, this operation requires a long time to determine the concentrations of dry soot and SOF. Therefore, it is very difficult to determine the rapidly changing concentrations as time passes; which is necessary for continuously regulating the exhaust gas from the diesel engine in a real time manner.
On the other hand, in U.S. Pat. No. 4,361,028, there is proposed a real time system for measuring particulates exhausted from a vehicle internal combustion engine by utilizing a so-called "dilution sampling method". However, according to this system, the dry soot and the SOF cannot be separately measured but are determined as a total amount.